Comment by ajarmst | Hacker News Reader

Comment by ajarmst | Hacker News Reader

Not a single interview with someone who actually understands how the systems work, nor any reference to any studies that show any results, positive or negative. Not one single "hey, so we set up a terrain avoidance radar and blasted it with variations of 5G communication and guess what?" (my suspicion is the answer would be "no effect", but let's at least do the study, huh?)

Radar altimeters use vastly more power than anyone would waste on mere communication. They also don't depend on subtle variations in the signal to communicate. It's basically just listening for a return and measuring time-of-flight. Timing measure is more complicated, but doesn't depend on subtleties of the signal that could be easily interfered with. (Full disclosure: I've worked on Herc terrain-avoidance radar, but that was forty years ago.)

Note also that commercial aviation pilots don't use terrain avoidance radar in normal flight operations. It's an emergency system. If you're low enough to need it, you're supposed to have an airport in sight. If you start getting the "Terrain. Pull Up" warning, several things have already been going wrong for a while. If you blocked the TAWS system of a commercial airline in normal flight, it's unlikely they'd even know it. You'd have to wait around for a lost or damaged aircraft that was already about to crash, which is a pretty unrewarding hobby.

To be honest, I'd be surprised if the military didn't already have a pretty good idea how to spoof terrain avoidance radar, it would be the kind of thing that might be nice to have in a special operations toolkit. But I doubt it looks like sitting on the end of a runway with a cell phone. More like humping several car batteries, a dish antenna and a Halliburton case full of electronics to the top of a ridge. (Which, another thing: terrain avoidance radar is the opposite of stealthy, you wouldn't use it for special operations, especially when you have access to GPS, satellite maps and inertial navigation systems).

Even a 5G transmission from ground to geosynchronous orbit would be columnated by a dish, so would only interfere with a moving altimeter for a fraction of a second, and those systems are designed to handle transients. I'm not saying there isn't a potential issue, I'm saying you're not going to find out if you limit yourself to interviewing bureaucrats.

Anything big (like an airliner) isn't allowed to rely on radio altimeter alone for terrain avoidance for many years now. They're GPS augmented. Whenever it is confident where it is (which will be always or almost always) the plane is deciding whether it could hit something by continuing to move apparently forward and alerting the pilots about that.

When you hear "Obstacle Obstacle" announced in Sully, that's not a radio altimeter detecting the bridge, the computer has concluded that the plane's motion is uncomfortably close to the bridge tower based on GPS and a database of tall things you might fly a plane into (and thus it knows this is an "Obstacle" whereas a mountain is "Terrain").

In that movie there's not a damn thing they can do beyond avoiding the bridge itself, because they don't have any thrust - but ordinarily pilots should near instinctively try to ascend immediately for any of this group of warnings. The training is specific that this is not the time for diagnostics, if you aren't already absolutely sure why the computer thinks you're about to hit something you must assume the computer is correct and climb at best rate. This routinely saves lives when pilots become confused about where they are.

Except in something like AirFrance 447 I guess?

There was no obstacle alert there. They just stalled.

Why do you even bother? I thought it was obvious by now this is propaganda to delay the adoption of 5G, allowing US competitors to catch up on Chinese equipment. The "concerns" are coming from bureaucratic positions no technically-savvy ones.

Indeed, if there is not a credible explanation from first principles it should be assumed that the article was written primarily for reasons other than illuminating knowledge.

Is there some evidence to support this idea that this is "obvious" propaganda? A plausible link, like what dog does the "Aerospace Industries Association" have in the 5G network hardware market?

From my not-very-informed perspective US competitors don't need to catch up to Chinese equipment, the Chinese equipment makers are locked out. If anything the US equipment makers would have the OPPOSITE motivation, get the spectrum sold and get their sub-standard equipment into the networks before the position of the US government could possibly change and they face real competition. And that is kind of what is happening, right? The actual story here is the FCC (lead by carrier and equipment friendly folks) are seemingly pushing ahead despite concerns from other industries, no?

The Chinese equipment might be locked out from the US market, but not from the world market. Unless the US could leverage the trust the world has on them to keep China from gaining market share. Remember they asked candidly the British to not buy China's 5G.

Also, not so long ago there were "reports" claiming Huawei devices were compromised and no evidence was provided. The negative marketing against China has been candid and in the open. The US is just trying to win in the court of public opinion on several fronts.

So yeah, "The military is scrambling to understand the aviation crash risk from a new 5G sale" and don't provide a technical basis for the concern: it reads propaganda all over.

I think China is effectively locked out of Western countries or at least US allies. The UK has banned Huawei and any purchased 5G equipment has to be decommissioned by 2027. Australia and NZ have also banned Huawei.

In this case the concern is with interference in the 4.0-4.2Ghz spectrum, nothing specific to 5G technology.

Is this frequency congested anywhere in the world with or without 5G technology to test?

But again, this doesn't really explain why US military hardware makers are concerned about this, unless the theory is that the US 5G equipment makers are pressuring the private industry groups that make military aviation equipment to pressure the US military and the FCC.. pretty far down a rabbit hole at this point with zero evidence.

And around the world 5G is not being deployed at the same frequencies! They are concerned about a particular spectrum. Lots of the purchased spectrum as I understand it is 30Gz+, they are raising zero concerns about that.

These are all good points, however just because this is a system that's only used in emergencies does not mean that this should be overlooked.

Just this year Kobe Bryant died because his helicopter impacted the terrain.

If this happened after the sale, you'd have to do just as difficult of an analysis to prove that 5G frequencies did not play a role in the impact, so why not do the analysis before hand?

I don't recall advocating not investigating this because the affected systems are emergency ones. I'm advocating against claiming there is danger without investigating ('abundance of caution' is usually shorthand for 'we could check this, but we're not going to bother and just make decisions without information because, hey, no one ever got fired for saying no, right?') My point is that even if there is potential issue that is highly unlikely, it will still have to line up with several other highly unlikely things for it to be a problem, which is a fairly good definition of 'safe' in modern complex systems engineering.

As to Kobe Bryant, yes his helicopter flew into terrain (unsurprisingly, 'flew into terrain' is incredibly common in aircraft accidents. Sadly, most of them are perfectly serviceable when they do so). There is no indication that the issue was a radar altimeter (if one was even installed, I don't believe they're required in that class), much less one that was being interfered with. I don't think the NTSB report is out yet, but I expect the cause will be what it commonly is: a pilot (with a famous and rich client who wanted to get somewhere quickly) taking their vehicle into marginal weather conditions beyond what they and their aircraft are competent to handle. Working on that problem will save a hell of a lot more lives than investigating 'may be a problem' that no one can even describe a mechanism for.

The Kobe crash could have been prevented by many things.

Existing synthetic vision systems would have easily prevented this. They're not even that expensive - built in systems can be had for a few tens of thousands of dollars, or non-certified iPad based systems for a few hundred.

That crash was likely due to disorientation in dense fog with an experienced, IFR rated pilot but who didn't experience much fog in LA. A radar altimeter would have been unlikely to help.

The Kobe crash could have been avoided by him driving his daughter to school rather than wasting resources on a helicopter every day.

And the potential car crash could be avoided by flying a helicopter. What kind of argument is this? I don't even think it's one.

I'm not really sure the 2020 Calabasa crash is a relevant example. That helicopter had a radio altimeter, and it surely wasn't being jammed. And before hitting the ground, the helicopter was descending at 20 m/s. The last known intent of the pilot was to climb, not descend. Some witnesses on the ground report that the helicopter sounded like it was malfunctioning before the crash. I do not particularly credit eye witnesses, but their story seems to fit with the rapid descent of the helicopter more than an altimeter issue.

Another point I should make about the Bryant crash (now that i've looked it up): while the pilot was IFR rated and the helicopter theoretically had the required instruments, the owning company was not certified for IFR passenger service. That means he the flight was filed as VFR. One of the things they teach you when you get an IFR rating is that you don't fly into IFR weather (IFC for the pedants) during a VFR flight without a pre-filed plan. His IFR training didn't teach him to fly in those conditions---it taught him to avoid them. They didn't have an IFR flight plan or clearance, so flying into a fog bank and persisting in that flight was forbidden and if unavoidable would constitute an emergency. Which is why I tend to look pretty hard at the pilot in this case, not the instruments.

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